It is known that organic and polymeric materials with large delocalized .pi.-electron systems can exhibit nonlinear optical response, which in many cases is a much larger response than by inorganic media.
Thin films of organic or polymeric materials with large second order nonlinearities in combination with silicon-based electronic circuitry have potential as systems for laser modulation and deflection, information control in optical circuitry, and the like.
Other novel processes occurring through third order nonlinearity such as degenerate four-wave mixing, whereby real-time processing of optical fields occurs, have potential utility in such diverse fields as optical communications and integrated circuit fabrication.
Of particular importance for conjugated organic systems is the fact that the origin of the nonlinear effects is the polarization of the .pi.-electron cloud as opposed to displacement or rearrangement of nuclear coordinates found in inorganic materials.
It is also known that an electromagnetic mechanism is an important contributor to surface-enhanced Raman scattering (SERS) and related surface optical phenomena. J. Phys. Chem., 91, 634 (1987) reports a method for measuring electromagnetic fields near the surfaces of small metal spheroidal particles to determine field and Raman enhancements for metals.
Optics Letters, 10, (No. 10), 511 (1985) describes surface-mediated enhancement of optical phase conjugation in metal colloids. The enhancement is attributed to the nonlinearities of the electrons in the metal particles, and the optical Kerr coefficients of gold and silver colloids are reported.
JETP Lett, 41 (No. 12), 616 (1985) describes second harmonic and size effects in colloidal metal particles. The publication states that the intensification of nonlinear optical processes at rough metal surfaces results from an increase in the local field due to the excitation of localized surface plasmons. Island films of silver are said to exhibit surface-enhanced Raman scattering, and the generation of a large second harmonic susceptibility.
Chem. Phys. Lett., 100 (No. 2), 163 (1983) reports that colloidal silver, dispersed in ethanol and stabilized with an adsorbed polymer such as polyvinyl pyrrolidone, exhibits enhanced Raman scattering of (N-4-dimethylaminoazobenzene-4'-sulfonyl) aspartate chromophore.
There is an increasing research effort to develop new nonlinear optical organic systems for prospective novel phenomena and devices adapted for laser frequency conversion, information control in optical circuitry, light valves and optical switches. The potential utility of organic materials with enhanced second order and third order nonlinearities for very high frequency application contrasts with bandwidth limitations of conventional inorganic electrooptic materials.
Accordingly, it is an object of this invention to provide novel optical media which exhibit nonlinear optical response.
It is another object of this invention to provide an organic-inorganic composite which exhibits nonlinear optical second order or third order nonlinear optical susceptibility.
It is a further object of this invention to provide a transparent solid composite of a polymer and a metal colloid which exhibits an enhanced nonlinear optical response.
Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.